Vibrational and Thermal Properties of Crystalline Topiramate

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

An Oligosilsesquioxane Cage Functionalized with Molybdenum(II) Organometallic Fragments

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

VCD to determine absolute configuration of natural product molecules: secolignans from Peperomia blanda

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Design of Gaussian basis sets to the theoretical interpretation of IR-spectrum of hexaaquachromium (III) ion, tetraoxochromium (IV) ion, and tetraoxochromium (VI) ion

The Generator Coordinate Hartree-Fock (GCHF) method is employed to design 16s, 16s10p, 24s17p13d, 25s17p13d, and 26s17p Gaussian basis sets for the H ((2)S), O ((3)P), O(2-) ((1)S), Cr(3+) ((4)F), Cr(4+) ((3)F), and Cr(6+) ((1)S) atomic species. These basis sets are then contracted to (4s) for H ((2)S), (6s4p) for O ((3)P), and O(2-) ((1)S), (986p3d) for Cr(3+) ((4)F), (10s8p3d) for Cr(4+) ((3)F), and (13s7p) for Cr(6+) (1S) by a standard procedure. For evaluation of the quality of those basis sets in molecular calculations, we have accomplished studies of total and orbital (HOMO and HOMO-1) energies at the HF-Roothaan level for the molecular species of our interest. The results obtained with the contracted basis sets are compared to the values obtained with our extended basis sets and to the standard 6-311G basis set from literature. Finally, the contracted basis sets are enriched with polarization function and then utilized in the theoretical interpretation of IR-spectrum of hexaaquachromium (III) ion, [Cr(H(2)O)(6)](3+), tetraoxochromium (IV) ion, [CrO(4)](4-), and tetraoxochromium (VI) ion, [CrO(4)](2-). The respective theoretical harmonic frequencies and IR-intensities were computed at the density functional theory (DFT) level. In the DFT calculations we employed the Becke's 1988 functional using the LYP correlation functional. The comparison between the results obtained and the corresponding experimental values indicates a very good description of the IR-spectra of the molecular ions studied, and that the GCHF method is still a legitimate alternative for selection of Gaussian basis sets. (C) 2003 Elsevier B.V. All rights reserved.

Structure control of poly(p-phenylene vinylene) in layer-by-layer films by deposition on a charged poly(o-methoxyaniline) cushion

In this paper, we demonstrate that the intrinsic electric field created by a poly(o-methoxyaniline) (POMA) cushion layer hinders the changes in molecular conformation of poly(p-phenylenevinylene) (PPV) in layer-by-layer with dodecylbenzene sulfonic acid (DBS). This was modeled with density functional theory (DFT) calculations where an energy barrier hampered molecular movements of PPV segments when they were subjected to an electric field comparable to that caused by a charged POMA layer. With restricted changes in molecular conformation, the PPV film exhibited Franck-Condon transitions and the photoexcitation spectra resembled the absorption spectra, in contrast to PPV/DBS films deposited directly on glass, with no POMA cushion. Other effects from the POMA cushion were the reduced number of structural defects, confirmed with Raman spectroscopy, and an enhanced PPV emission at high temperatures (300 K) in comparison with the films on bare glass. The positive effects from the POMA cushion may be exploited for enhanced opto-electronic devices, especially as the intrinsic electric field may assist in separating photoexcited electron-hole pairs in photovoltaic devices. © 2013 American Institute of Physics.

Espécies metalo-supramoleculares discretas polinucleares: sínteses e caracterização

Pós-graduação em Química - IQ

Manganese(II) complexes with thiosemicarbazones as potential anti-Mycobacterium tuberculosis agents

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Toward an Understanding of the Growth of Ag Filaments on alpha-Ag2WO4 and Their Photoluminescent Properties: A Combined Experimental and Theoretical Study

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Stretching of BDT-gold molecular junctions: thiol or thiolate termination?

It is often assumed that the hydrogen atoms in the thiol groups of a benzene-1,4-dithiol dissociate when Au-benzene-1,4-dithiol-Au junctions are formed. We demonstrate, by stability and transport property calculations, that this assumption cannot be made. We show that the dissociative adsorption of methanethiol and benzene-1,4-dithiol molecules on a flat Au(111) surface is energetically unfavorable and that the activation barrier for this reaction is as high as 1 eV. For the molecule in the junction, our results show, for all electrode geometries studied, that the thiol junctions are energetically more stable than their thiolate counterparts. Due to the fact that density functional theory (DFT) within the local density approximation (LDA) underestimates the energy difference between the lowest unoccupied molecular orbital and the highest occupied molecular orbital by several electron-volts, and that it does not capture the renormalization of the energy levels due to the image charge effect, the conductance of the Au-benzene-1,4-dithiol-Au junctions is overestimated. After taking into account corrections due to image charge effects by means of constrained-DFT calculations and electrostatic classical models, we apply a scissor operator to correct the DFT energy level positions, and calculate the transport properties of the thiol and thiolate molecular junctions as a function of the electrode separation. For the thiol junctions, we show that the conductance decreases as the electrode separation increases, whereas the opposite trend is found for the thiolate junctions. Both behaviors have been observed in experiments, therefore pointing to the possible coexistence of both thiol and thiolate junctions. Moreover, the corrected conductance values, for both thiol and thiolate, are up to two orders of magnitude smaller than those calculated with DFT-LDA. This brings the theoretical results in quantitatively good agreement with experimental data.

Freezing Distortions and Photoluminescence Property in PbMoO4 Micro Octahedrons: An Experimental and Theoretical Study

In this paper, we report a detailed structural and electronic characterization of PbMoO4 crystals by using a conventional hydrothermal (CH) method. The samples were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), field-emission gun scanning electron microscopy (FEG-SEM) and photoluminescence (PL) measurements. In addition, first-principles quantum mechanical calculations based on the density functional theory were employed in order to understand the band structure and density of states for the PbMoO4. Analysis of both theoretical and experimental results allows to rationalize the role of order-disorder effects in the observed green PL emissions in these ordered powders.

A joint experimental and theoretical study on the electronic structure and photoluminescence properties of Al-2(WO4)(3) powders

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Antitubercular activity of Ru (II) isoniazid complexes

Despite the resistance developed by the Mycobacterium tuberculosis (MTb) strains, isoniazid (INK) has been recognized as one of the best drug for treatment of Tuberculosis (Tb). The coordination of INH to ruthenium metal centers was investigated as a strategy to enhance the activity of this drug against the sensitive and resistant strains of MTb. The complexes trans-[Ru(NH3)(4)(L)(INH)](2+) (L = SO2 or NH3) were isolated and their chemical and antituberculosis properties studied. The minimal inhibitory concentration (MIC) data show that [Ru(NH3)(5)(INH)](2+) was active in both resistant and sensitive strains, whereas free INK (non-coordinated) showed to be active only against the sensitive strain. The coordination of INH to the metal center in both [Ru(NH3)(5)(INH)](2+) and trans-[Ru(NH3)(4)(SO2)(INH)](2+) complexes led to a shift in the INH oxidation potential to less positive values compared to free INH. Despite, the ease of oxidation of INH did not lead to an increase in the in vitro INH activity against MTb, it might have provided sensitivity toward resistant strains. Furthermore, ruthenium complexes with chemical structures analogous to those described above were synthesized using the oxidation products of INK as ligands (namely, isonicotinic acid and isonicotinamide). These last compounds were not active against any strains of MTb. Moreover, according to DFT calculations the formation of the acyl radical, a proposed intermediate in the INH oxidation, is favored in the [Ru(NH3)(5)(INH)](2+) complex by 50.7 kcal mol(-1) with respect to the free INH. This result suggests that the stabilization of the acyl radical promoted by the metal center would be a more important feature than the oxidation potential of the INH for the antituberculosis activity against resistant strains. (C) 2015 Elsevier B.V. All rights reserved.

Estrutura eletrônica de derivados de politieno[3,4-b]-tiofeno-co-benzoditiofeno para aplicação em camadas ativas de células solares orgânicas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

DFT study of alpha-alanine as a function of the medium polarity

The zwitterionic (Z) form, neutral (N) form and transition structure (TS) connecting N to Z, have been studied at the B3LYP/6-31++G** level of calculation by using the SCRF methodology. The intramolecular proton transfer from oxygen to nitrogen atoms of alpha -alanine and vibrational spectrum were analyzed in the different environments employed: acetonitrile, ethanol, carbon tetrachloride and gas phase. The Z species is a stationary point in acetonitrile and ethanol, but not in carbon tetrachloride and gas phase media. The geometry of N, Z and TS was similar in acetonitrile and ethanol. The vibrational spectrum of Z was similar in the two solvents studied. (C) 2001 Elsevier B.V. B.V. All lights reserved.

Antioxidant Properties of Plant Extracts: an EPR and DFT Comparative Study of the Reaction with DPPH, TEMPOL and Spin Trap DMPO

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)